Two-phase endolymphatic hydrops: A new dynamic model for Meniér's disease

In 1861, Prosper Meniere described the classical triadic symptomatology of hearing loss, vertigo and tinnitus, which he attributed for the first time to a labyrinthine disorder. The underlying pathophysiology of this disabling inner ear disease was not known, but since Hallpike and Cairns, and also Yamakawa in 1938 discovered hydrops of the endolymphatic system in the temporal bones of patients with Meniere’s disease, endolymphatic hydrops has been generally accepted as the basic histopathological substrate of Meniere’s disease. Endolymphatic hydrops may arise as a result of the destabilization of natural regulation through overproduction of endolymph and/or reduced absorption of endolymph. Total destruction of the endolymphatic sac, which is considered to be responsible for the absorption of endolymph, and obliteration of the vestibular aqueduct, resulted in endolymphatic hydrops in the guinea pig, and has been established as the classical guinea pig model for Meniere’s disease (Kimura, 1965). However, obliteration of the vestibular aqueduct is regarded as a non-physiological model for Meniere’s disease. In patients with Meniere’s disease, endolymphatic sac tissue still remains present, although the size of the endolymphatic sac is reduced, suggesting a reduction in resorptive capacity. The production of endolymph is thought to be regulated by Na/K-ATPase in the marginal cells of the stria vascularis of the cochlea, as well as in the dark cells of the utricle and the cristae ampullares of the semicircular canals. In recent experiments, a relationship between circulating adrenal steroids and Na/K-ATPase activity in the inner ear was observed. Emotional stress leads to the activation of neuroendocrine effector systems, including the production of adrenal steroids such as aldosterone, and could thus increase the production of endolymph. A borderline capacity of the ES, in combination with a periodic increase of endolymph production caused by stressful situations may be responsible for the development of Meniere’s disease. Indeed, manifestations of Meniere’s disease frequently occur during stressful experiences in patients with physiological systems under challenge due to a neurasthenic psychological profile. We developed the two-phase endolymphatic hydrops model in guinea pigs which was based on two compromising fators; mild chronic endolymphatic sac dysfunction has been established by dissection of the distal part of the endolymphatic sac from the sigmoid sinus, in combination with periodic increase of endolymph production by stimulation of the Na/K-ATPase pumps in the stria vascularis by administration of aldosterone. This model, which seemed to represent a functional model combining multiple etiologies, and may resemble the fluctuant characteristics of Meniere’s disease.